Time-based effects (reverbs, delays, modulation and flangers, among others) can provide you with a real opportunity to personalize your mix. These effects can be mild or cut loose to see how far they can be taken. Below is a quick breakdown of some popular time-based effects, and how to use them during your recording sessions. 
Reverb
Reverberation will be created when echoes build up until they are absorbed by the space. Delay is the basic form of reverb, with a lot of delays offering reverb settings, too. In the digital world, reverbs will usually reside on aux channels, which are automatable, and in the analog world they will be sent from aux sends and returned to a channel on the console so that it can be automated. A pre-delay setting will control the amount of time before the actual reverb begins. This will give a little space between the original source signal and the reverb tail. Reverb time settings will control the amount of time that the reverb takes to decay – the amount of time the reverb tail will take to fade out, or RT60, the amount of time to decay by 60dB). Diffusion is the how the sound spreads out through the emulated space, with areas of higher and lower concentration.
There are many different types of reverbs made by many companies, so finding one that best suits your needs will be the key to avoid becoming overwhelmed by the number of choices. Plate Reverbs use a piece of sheet metal to produce the reverb. Once the transducer sends the direct signal to the sheet metal, it will begin to vibrate. Plate Reverb can be controlled with a dampening pad. The closer the pad moves to the sheet metal, the shorter the reverb time will be; it will never let the pad touch the metal or it will kill the vibrations, which in turn will stop the reverb. Spring Reverbs operate similarly to plate reverbs, where there will be a transducer at one end and a spring on the other. When the direct signal passes through, the spring will vibrate and the pickups will be used to output the signal. Digital reverbs will use algorithms to create a reverb effect, most of which can emulate physical spaces (rooms, halls etc) by calculating room shape, size, ceiling heights, diffusion, etc. Digital reverbs often offer more customization, but can be more time consuming to program.
Reverbs will usually consist of a mono input and stereo output. The newest reverb on the scene is convolution reverb. These use impulse responses to create the convolution – by doing this they are able to create a realistic representation of the space. An impulse response is the reverb that will occur when an impulse signal is produced and then recorded through a test microphone into a software program that will store the information. This gives a relatively large number of options to spaces that can be made into convolutions. Convolution reverbs can also be used to model older reverb units, opening up even more options. As computer processing has become more efficient, so has the operation of this style of reverb. These are still processor hogs compared to other reverb plug-ins, but the options are vast, giving the opportunity to craft more realistic spaces for the mix.
Delays
Delays are pretty simple in the way in which they work. The earliest delay units were made by utilizing reel-to-reel tape units, judging the length of the tape and adjusting the read/write head. As its most basic function, a delay will take and input a signal, hold for a specified time and then it output it. Digital delays were introduced in the ’80s, providing users with more options and more control. Many of these vintage units are available today as plug-ins, offering a cheaper and more user-friendly option for engineers accustomed to computer-based recording.
In the mix, the delay can add space or can be used to thicken up a source. When used as a thickening agent, the delay can be put directly on the source channel and mixed between wet and dry amounts. Depending on the delay, the controls will be pretty straightforward. Input will be a gain stage for the input signal, wet and dry will judge the mix between the direct and affected signal, and feedback will send some of the output signal back to the input, causing the delay to repeat (a really common effect on any U2 record).
Chorus
Chorus is achieved when the original signal feeds a delay that is also setup with modulation. This will smear the tuning of the chorused source, thickening it up. This effect can sound very close to flanging. Chorus usually features a slightly longer delay (25-50 milliseconds) and does not have a feedback control. Flange effects have shorter delay times, usually 10-25 milliseconds. Flanging is the result of two identical sources, with one’s delay slowly changing and being sent through an LFO. The LFO will modulate the source that has been delayed. These will usually come with feedback, and vibrato effects will use the LFO to modulate the frequency of the delayed source. A phaser is a filter type of effect that will have a series of peaks and troughs, modulating the audio and then mixing it back with the original source. This will cause phasing in different frequencies at different times, creating a “sweeping” or “whooshing” effect in the frequency spectrum. Think early Van Halen guitar sounds.
Final Notes
There are many choices with time-based effects, whether you are looking at the rack mount, pedal, or plug-in versions. Just remember that these items are simply tools in the toolbox; they represent your chance to expand the horizons of your audio and should be used to suit the project.
When using time-based effects in plug-in form, all parameters are typically automatable, which can aid in mixing different sections of a song. If processor power becomes an issue, you can always print the effect down to an audio channel and deactivate the aux track with a plug-in on it.